Ceramic thin film on various substrates, and process for producing same

ABSTRACT

The process of Polymer Assisted Chemical Vapor Deposition (PACVD) and the semiconductor, dielectric, passivating or protecting thin films produced by the process are described. A semiconductor thin film of amorphous silicon carbide is obtained through vapor deposition following desublimation of pyrolysis products of polymeric precursors in inert or active atmosphere. PA-CVD allows one or multi-layers compositions, microstructures and thicknesses to be deposited on a wide variety of substrates. The deposited thin film from desublimation is an n-type semiconductor with a low donor concentration in the range of 10 14 -10 17  cm −3 . Many devices can be fabricated by the PA-CVD method of the invention such as; solar cells; light-emitting diodes; transistors; photothyristors, as well as integrated monolithic devices on a single chip. Using this novel technique, high deposition rates can be obtained from chemically synchronized Si—C bonds redistribution in organo-polysilanes in the temperature range of about 200-450° C.

FIELD OF THE INVENTION

The present invention relates to a ceramic thin film which may be anamorphous silicon carbide (a-SiC) semiconductor thin film deposited onvarious substrates suitable for photovoltaic cells and a variety ofrelatively high performance low-cost electronic devices which can beeasily and economically mass-manufactured. By means of Polymer-AssistedChemical Vapor Deposition (PA-CVD), new semiconductor materials withhigh conversion yields can be produced at low cost. The process involvesgaseous precursors from polymeric sources, which lead to chemicallysynchronized construction of a desirable amorphous silicon carbidestructural framework with special electronic and photonic properties.

BACKGROUND OF THE INVENTION

Kitabatake et al., disclose in U.S. Pat. No. 6,270,573 B1, CVD andCVD-related methods of producing silicon carbide substrates, includingthe growing of silicon carbide film by supplying separate silicon atomsand carbon atoms on a surface. The silicon-carbon bond formation occursmainly on the surface of the substrate, a step that usually requireshigh temperatures, in this particular case the required temperaturebeing 1300° C. MBE and MO-CVD may use species that contain a limitednumber of pre-existing Si—C bonds in the precursor, this number beingusually related to precursor synthesis requirements.

Kong et al. (European Patent No. EP 0,970,267) describe a susceptordesign for silicon carbide resulting in minimizing or eliminatingthermal gradients between the two surfaces of a substrate wafer. The CVDand CVD-related deposition procedures of Kong et al., require strictcontrol of the temperature field and the gas flow at the surface of thesubstrate, where the Si—C bond formation is occurring.

Grigoriev et al. (Grigoriev, D. A., Edirisinghe, M. J., Bao, X., Evans,J. R. G. and Luklinska, Z. B.(2001) “Preparation of silicon carbide byelectrospraying of a polymeric precursor,” Philosophical MagazineLetters (UK), 81, 4, 2001 by Dept. of Mater., Queen Mary Univ. ofLondon, UK) present silicon carbide coatings and films prepared for thefirst time by electrostatic atomization of a solution of a polymericprecursor and deposition onto alumina and zirconia substrates. In themethod of Grigoriev et al., the polymeric source already contains mostof the Si—C bonds required for the formation of the SiC film; however,the molecular source is carried to the surface inside cages of solventmolecules, implicitly leading to contamination of the film, shrinkingand outgassing phenomena, due to solvent evaporation and polymercracking. These effects will be present in any polymer-assisted method(spin-coating, spraying, laser ablation . . . ).

Lau et al. (Lau, S. P., Xu, X. L., Shi, J. R., Ding, X. Z., Sun, Z. andTay, B. K. (2001) “Dependences of amorphous structure on bias voltageand annealing in silicon-carbon alloys,” Materials Science &Engineering, B85 (16), Sch. of Electr. & Electron. Eng., NanyangTechnol. Inst., Singapore) report on amorphous silicon-carbon alloyfilms that have been obtained by filtered cathodic vacuum arc (FCVA)technique. They have observed that the disorder of the Si—C networkincreased with using the high bias voltages during the deposition. Thishigh disorder in the film with high bias voltages induces the smallernanometer crystallites after annealing at 1000° C. rather than low bias.The Raman peaks shift to the high frequency with increasing theannealing temperature up to 750° C. due to the increase of nanometergrain size at the same bias. A sharp transition from nanocrystalline topolycrystalline can be observed when the films are annealed under 1000°C.

Jana of al. (Jana, T., Dasgupta, A. and Ray, S. (2001) “Doping of p-typemicrocrystalline silicon carbon alloy films by the very high frequencyplasma-enhanced chemical vapor deposition technique” Journal ofMaterials Research, 16(7) 2001, 2130-5, Energy Res. Unit, Indian Assoc.for the Cultivation of Sci., Calcutta, India) present the synthesis ofp-type silicon-carbon alloy thin films by very high frequencyplasma-enhanced chemical vapor deposition technique using a SiH₄, H2,CH₄, and B₂H₆ gas mixture at low power (55 mW/cm²) and low substratetemperatures (150-250° C.). Effects of substrate temperature and plasmaexcitation frequency on the optoelectronic and structural properties ofthe films were studied. A film with conductivity 5.75 Scm⁻¹ and 1.93 eVoptical gap E₀₄ was obtained at a low substrate temperature of 200° C.using 63.75 MHz plasma frequency. The crystalline volume fractions ofthe films were estimated from the Raman spectra. They observed thatcrystallinity in silicon carbon alloy films depends critically on plasmaexcitation frequency. When higher power (117 mW/cm²) at 180° C. with 66MHz frequency was applied, the deposition rate of the film increased to5.07 nm/min without any significant change in optoelectronic properties.

Yamamoto et al. (Yamamoto et al., Diam. Relat. Mater., vol. 10 (no.9-10), 2001, pp. 1921-6) present a doping procedure whereby amorphousSiCN films were prepared on Si (100) substrates by nitrogen ion-assistedpulsed-laser ablation of a SiC target. The dependence of the formedchemical bonds in the films on nitrogen ion energy and the substratetemperature was investigated by X-ray photoelectron spectroscopy (XPS).The fractions of Sp² C—C, Sp³ C—C and Sp² C—N bonds decreased, and thatof N—Si bonds increased when the nitrogen ion energy was increasedwithout heating during the film preparation.

The fraction of sp C—N bonds was not changed by the nitrogen ionirradiation below 200 eV. Si atoms displaced carbon atoms in the filmsand the Sp³ bonding network was made between carbon and silicon throughnitrogen. This tendency was remarkable in the films prepared undersubstrate heating, and the fraction of sp³ C—N bonds also decreased whenthe nitrogen ion energy was increased. Under the impact of high-energyions or substrate heating the films consisted of Sp² C—C bonds and Si—Nbonds, and the formation of Sp³ C—N bonds was difficult. The Yamamotoprocedure proposes a doping step separate from the synthesis step.

Budaguan et al. (Budaguan, B. G.; Sherchenkov, A. A.; Gorbulin, G. L.;Chernomordic, V. D. (2001) “The development of a high rate technologyfor wide-bandgap photosensitive a-SiC:H alloys,” Journal of Alloys andCompounds, 327(30) Aug., 146-50, Inst. of Electron Technol., Moscow,Russia) discuss in their paper the deposition process and the propertiesof a-SiC:H alloy fabricated for the first time by 55 kHz PECVD. It wasfound that 55 kHz PECVD allows an increase in the deposition rate ofa-SiC:H films.

Modiano et al. (Japanese patent No. 145138/95) present a process forproducing silicon carbide fibers having a C/Si molar ratio from 0.85 to1.39, comprising the steps of rendering infusible the precursory fibersmade from an organosilicon polymer compound, then primarily baking theinfusible fibers in a hydrogen gas-containing atmosphere. This processfor producing silicon carbide thin films comprises the steps ofimparting semiconductor properties to passivating or dielectric thinfilms from volatile precursory species produced from organosiliconpolymer compounds.

Yang et al. (Yang, Lixin; Chen, Changqing; Ren, Congxin; Yan, Jinlong;Chen, Xueliang, “Synthesis of SiC Using Ion Beam and PECVD”,International Conference on Solid-State and Integrated CircuitTechnology Proceedings, pp. 811-814) present a process for producingsilicon carbide thin films comprising the steps of conferringsemiconductor properties to passivating or dielectric thin films fromvolatile precursory species produced from organosilicon polymericcompounds.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to provide a method ofdepositing a thin ceramic film on an appropriate substrate.

Another object of the present invention is to provide a ceramic thinfilm deposition on a substrate.

It is a further object is to provide a semiconductor device comprisingthe film according to invention.

In accordance with one embodiment of the invention there is provided amethod of depositing a thin ceramic film onto a substrate comprising:providing a polymeric source; providing the substrate; heating thepolymeric source under a gaseous atmosphere having a pressure and aflowrate, whereby pyrolyzing the polymeric source to produce a gaseousprecursor at a first temperature comprising chains of the polymericsource; positioning the substrate to receive the gaseous precursorcarried by the gaseous atmosphere; and cooling the substrate at a secondtemperature below the first temperature whereby desublimating thegaseous precursor onto the substrate, the precursor chemicallyrearranging and annealing to produce the film on the substrate, the filmhaving properties that include an amorphous nature, a crystallinity anda degree of reticulation.

In accordance with another embodiment of the invention there is provideda ceramic thin film deposited on a substrate comprising chains from apolymeric source that have been deposited on the substrate andchemically rearranged and annealed wherein the film is essentially freeof defects.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of preferred embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schema of the Polymer-Assisted Chemical Vapor Depositionreactor;

FIG. 1 b is a temperature-profile in the reactor versus the distancefrom the gas input;

FIG. 2 is a representation of the set of chemical reactions leading ton-type a-SiC from a generic polysilane precursor (polymethylsilane,e.g.) within the reactor;

FIG. 3 is a series of various substrates supporting PA-CVD films;

FIG. 4 illustrates an infrared spectrum of a gaseous precursor formedduring deposition of a-SiC PA-CVD films;

FIG. 5 is a design of the FT-IR cell based on a silicon single crystalwafer, designed for the monitoring of a film produced by the PA-CVDprocess;

FIG. 6 illustrates the carrier properties of the n-type PA-CVD depositeda-SiC film;

FIG. 7 illustrates the semiconductor properties of the n-type PA-CVDdeposited a-SiC film;

FIG. 8 illustrates the FT-IR spectrum a silicon nitride PA-CVD depositedfilm;

FIG. 9 illustrates the FT-IR spectrum a silicon oxycarbide PA-CVDsynthesized film;

FIG. 10 illustrates a simple Schottky solar cell;

FIG. 11 is a p-n junction barrier photovoltaic cell based on a-SiC;

FIG. 12 illustrates a stacked p-n junction solar cell;

FIG. 13 a illustrates an energy band diagram of Schottky structurebefore intimate contact between metal and semiconductor;

FIG. 13 b illustrates an energy band diagram of Schottky structure afterintimate contact between metal and semiconductor; and

FIG. 14 illustrates the energy band of a p-n junction solar cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present description refers to a number of documents, the content ofwhich is herein incorporated by reference in their entirety.

An aspect of the present invention is concerned with an innovativemethod of forming volatile pyrolysis products from Si-based polymericcompounds or sources. These sources can be used to form gaseousprecursors to thin films of ceramic materials insilicon-carbon-nitrogen-oxygen systems that can be deposited on commonlyavailable substrates as a completely to partially amorphoussemiconductor, at a desired micron-range thickness, onto a variety ofcommonly available and resistant substrates of varying composition,degree of stiffness, shape, density, color, etc., over a small to anexceptionally large surface. This method is herein calledPolymer-Assisted Chemical Vapor Deposition (PA-CVD). The thin filmsproduced by the method will be durable, may be flexible (due to theirthinness), and can be used for high-performance semi-conductors. Thefilm may be deposited on a small as well as a large surface substrates.The substrates can be rigid or highly flexible and of variouscomposition, shape, thickness and color.

According to the present invention, during PA-CVD (PolymerAssisted-Chemical Vapor Deposition), most of the Si—C bonds required forthe formation of the silicon carbide structure pre-exist in thepolymeric source. Because most of the Si—C bonds pre-exist in thepolymeric source and gaseous precursor produced therefrom, thetemperature requirements become more flexible, allowing lowertemperatures and expanded operational range. For this reason the natureof the substrate is less important, in terms of thermal stability, sizeor shape. More than 50% of the SiC bonds pre-exist in the polymericprecursor. Furthermore, the gaseous precursor is deposited in chemicalchains, similar to physical chains, that then rearrange and bind to oneanother. The bond formed between the precursor and the substrate is avan der Waals physical bond.

The PA-CVD method of the present invention further distinguishes itselffrom other forms of CVD because it does not require solvent molecules todissolve the precursor, the evaporation of these solvents in other CVDmethods produces defects on the surface of the coating they produce,this is one reason why the PA-CVD method produces films with fewer andessentially no surface defects.

PA-CVD further allows the polymeric source to self-adjust to thetemperature field because each polymeric source will develop a set ofgaseous precursors adapted to the particular thermal conditions (variousgradients and temperature-cycles produce different gaseous precursors,thermodynamically stable under the specific conditions). This selfadjustment is different for different polymeric sources. The net resultis that PA-CVD produces pure gaseous precursors, containing a maximumnumber of pre-existing Si—C bonds thermodynamically stable in the localexisting conditions, thus minimizing the extent of the chemical reactionrequired for completion of the silicon carbide structure at the surfaceof the substrate. In this process, the polymer pyrolysis mechanismsnaturally leave in the solid residue the usually larger molecular weightspecies containing adventitious oxygen (such as siloxane species), whilethe gaseous precursors reaching the substrate are less contaminated.

The PA-CVD of the present invention allows reduced depositiontemperatures because a majority of the Si—C bonds pre-exist in theprecursor. PA-CVD also uses in-situ doping (N, P, As, B, . . .containing gas-phase species that react chemically with the precursorbefore deposition) allowing in-situ determination of the dopantconcentration and monitoring of the formation of dopant-containingspecies (aminosilane formation via IR spectroscopy could be performeddirectly in the quartz reactor). PA-CVD locks the carbon atoms in a Sp³hybridization state process of the present invention. PA-CVD allowssignificantly higher deposition rates when used on very large substratesas compared with the a-SiC films produced by any other CVD-relatedmethod, including that taught by the aforementioned Budaguan et al.

The PA-CVD process according to the present invention:

-   1) allows for the hydrogenation, heat treatment and makes full use    of many different types of gaseous reactants such as, B₂H₆, NH₃,    PH₃, AsH₃, BCl₃, B₂Cl₆, NCl₃, PCl₃, AsCl₃,CO, O₂, O₃, CO, CO₂, as    well as H₂ pure or inert carried gases such as Ar or N₂, or similar    mixtures, with the inert gases varying from 0.1 to 99.0 % in volume;-   2) can accommodate a wide variety of heat sources and treatment    lengths for the polymeric precursors or for the deposited film under    the gaseous atmospheres, for as little as 1 second and up to, but    not limited to, tens of hours, and leading to a wide variety of    passivating, semiconductor, and dielectric thin film materials;-   3) allows secondary annealing under BH₃, B₂H₆, NH₃, PH₃, AsH₃, BCl₃,    B₂Cl₆, NCl₃, PCl₃, AsCl₃, CO, O₂, O₃, CO, CO₂ or H₂ gases for    several seconds, thereby increasing the crystallinity and/or the    degree of reticulation of the deposited film;-   4) the PA-CVD process can make good use of standard heating methods    as well electronic beams, X-rays, UV and IR radiation microwave    power, laser beams and other energy transfer mechanisms to produce    objects and substrates in flat, or tubular or complex shapes    including, but not restricted to, rods, cylinders, spheres, ceramic    boats, etc.; and-   5) produces substrates with varying conductor, semiconductor or    dielectric properties, including, but not restricted to    polycrystalline or amorphous silicon; quartz; graphite; metals;    electronic-grade or refractive ceramic materials, such as alumina or    sintered oxides, nitrides, phosphides;.as well as A₂B₆, A₃B₅,    ternary and quaternary compounds in this class.

The PA-CVD process does not require massive silicon-carbon bondformation on the surface of the substrate, since most of the existingSi—C network in the amorphous phase is obtained via massive Si—C bondredistribution during processes preceding the deposition of the thinfilm.

The PA-CVD design allows the use of a broad series of polymericprecursors for use in the synthesis of silicon-based thin filmsincluding, but not limited to, oxides, nitrides, carbides and variouslyweighted combinations in homogeneous phases or multi-layered structures.The resulting films are of considerable interest as electronic andoptoelectronic materials as well as for protective coatings. A largevariety of appropriate silicon-based polymeric sources can be used, suchas polysilanes, polycarbosilanes, polycarbosilazanes, polysiloxanes andpolysiloxazanes. Other appropriate polymeric sources include: carbonnitride polymeric sources and boron nitride polymeric sources which toohave been found to produce useful ceramic products. The possible carbonnitride polymeric sources (CxNy) include: polyepoxy-, polyamides,polyamines, polyimides, polyureas and polyurethanes. It is noted thatpolyamides, polyamines, polyimides and polyureas can be used in mixtureswith the other polymeric sources and as a possible source of nitrogen inthe reaction. Polymers sources with other backbones can be envisagedcomprising: Al, B, Ge, Ga, P, As, N, In, Sb, S, Se, Te, In and Sb.

By means of p-n homo- or heterojunctions and using a variety of flexibleor rigid substrates, it is possible to fabricate solar cells,light-emitting diodes, transistors, photothyristors, and similardevices. Using high breakdown electrical field and high electronsaturation velocity, it is further possible to produce high frequency,high power and high temperature electronic and optoelectronic devices.By combining optical and electronic properties, the materials may alsoserve to fabricate integrated monolithic devices on a single chip.

The PA-CVD process is relatively simple requiring only a driving forcegenerated in the furnace (2), being the supersaturation ratio obtainedin a temperature gradient field. Furthermore, PA-CVD distinguishesitself from other forms of chemical vapor deposition because it does notrequire the following more sophiscated driving forces:

-   a) ion implantation, ion beam enhanced deposition, reactive ion beam    sputtering and plasma enhanced chemical vapor deposition (PECVD);-   b) RF power (as described in “High temperature annealing of    hydrogenated amorphous silicon carbide thin films” INS 01-17 6910830    A2001-11-6855-060 (PHA) NDN-174-0691-0829-5 Yihua Wang; Jianyi Lin;    Cheng Hon Alfred Huan; Zhe Chuan Feng; Soo Jin Chua);-   c) IR and UV laser photolysis (as described in “Laser gas-phase    photolysis of organosilicon compounds: approach to formation of    hydrogenated Si/C, Si/C/F, Si/C/O and Si/O phases” INS 00-50 6791677    A2001-03-8250F-001 (PHA) NDN-174-0679-1676-1 Pola, J. JOURNAL NAME-    PINSA-A (Proceedings of the Indian National Science Academy) Part A    (Physical Sciences)); and-   d) electron cyclotron resonance ( as described in “Application of    electron cyclotron resonance chemical vapor deposition in the    preparation of hydrogenated SiC films. A comparison of phosphorus    and boron doping” INS 98-04 5814339 A98058115H-021 (PHA);    B9803-0520F-017 (EEA) NDN-174-0581-4338-2 Yoon, S. F.; Ji, R.).

An reactor (2), for PA-CVD is illustrated in FIG. 1 a which shows theprincipal characteristics of a reactor that can be used for PA-CVD,while FIG. 1 b illustrates the varying temperature profile within thePA-CVD reactor.

Referring to FIG. 1A, there is a quartz reactor (2), into which one orseveral polymer derived precursors (19), enter through gas inlet (1).The quartz reactor (2) is also referred to as the furnace or the PA-CVDreactor. Furthermore, a gaseous atmosphere (60), either inert or active,also enters through the gas inlet (1). The inert atmosphere includesargon, nitrogen or other inert gases. While the active atmosphereincludes gases such as ammonia, carbon monoxide or similar gases. Beforeoperation the reactor (2) is purged with a selected atmosphere (60).

The gas inlet (1), has a high-vacuum seal to minimize the ingress ofoxygen impurities from the surrounding air drawn into the reactor (2).The total pressure in the reactor is measured with a pressure controller(3) which also controls the flowrate into the reactor (2). The outsideof the reactor is heated with electric heating elements (4), whichsurround the PA-CVD reactor (2) to produce the temperature gradientillustrated in FIG. 1 b. There are more heating elements (4) near theinlet of the reactor (2), while there are fewer surrounding thedeposition area of the reactor. The PID(Proportional-Integral-Derivative) temperature controller (5), ensuresthat the temperature within the reactor (2) is in the appropriate rangefor the polymer-derived precursor (19) used, the type of gaseousatmosphere (60) and substrate (6) to be coated. The substrate (6), isplaced in the deposition area of the reactor (2). Typically thesubstrate (6), is a piece or part made of silicon, quartz, metal,ceramics, etc. The gas phase near the gas outlet (9), of the reactor(2), is analyzed by an FT-IR (Fourier Transform InfraRed) spectrometer(7). The FT-IR spectrometer (7), allows the in situ verification of thedeposition process and the oxygen impurities present. A SiC film (8) isdeposited on the substrate (6) through the decomposition of the siliconbased polymeric sources (19) and their chemical rearrangement to SiC onthe surface of the substrate (6). The deposited film (8) can be a singleor multiple layered film.

Referring to FIG. 1B, the temperature profile within and along thelength of the reactor (2) is represented. The input zone (10) shows aconstant lower temperature associated with the gas inlet (1). In theheating zone (11), there is a increase in the temperature due to thelarge amount of heating elements (4) at the inlet. In the heating zone(11), the rearrangement of the silicon based polymeric sources occurswhich leads to the formation of the poly(carbosilane) species. The nexttemperature is that of the pyrolysis zone (12), where there is directprecursor formation and doping occurring. This is followed by areduction in the number of heating elements (4) in the deposition zone(13) which consequently cools the particularly zone of the reactor (2)thus lowering the temperature. The deposition zone (13) is representedby a constant temperature while the SiC is being deposited on thesubstrate (6). Finally there is the gas exit zone (14), where thetemperature falls in the gas outlet (9) of the reactor (2) andapproaches that of the ambient temperature outside the reactor (2). Thetemperatures in the reactor (2) and represented in FIG. 1B, vary from100 to 1000° C. In a preferred embodiment the PA-CVD temperature zonevaries from 200 to 450° C.

The PA-CVD process and resulting materials produced are based on theinnovative design and directed behaviour of volatile, relatively largemolecular mass, gaseous precursors derived from silicon-based polymericsources. This PA-CVD synthesis of inorganic thin silicon-based filmsincludes silicon carbide, silicon nitride, silicon oxide, siliconoxycarbide, silicon oxynitride, silicon oxycarbonitride and other suchmaterials, in pure and doped forms.

The tolerance of the polymeric source to depolymerization processes isrelated directly to silicon-carbon, silicon-nitrogen and silicon-oxygenrelative bond stability in the above-mentioned precursors (19), in agiven thermal environment resulting from given inert or active pyrolysisconditions. This PA-CVD process was tested by subjecting the classes ofabove-mentioned various silicon-based polymers to various thermalbudgets controlling the depolymerization conditions (thermal cracking,chemical decomposition and polymeric disproportionation). The depositedfilms can be used as active, passivation, dielectric or protectivecoatings for semiconductor discrete or integrated devices or implantablematerials. Any combination of these categories of pure or dopedmaterials can be deposited on metals, ceramics, glasses or plastics, insingle- or multiple-layered structures, at temperatures above 300° C.

The resulting semiconductor thin film possesses highly desirableelectronic, optoelectronic and photonic properties that make it highlysuitable for standard, cost-effective fabrication of a variety ofelectronic and optoelectronic devices, including photovoltaic cells. Thea-SiC thin film is an n-type and/or p-type mono or heterojunction with adonor concentration of 10¹⁴-10¹⁷ cm⁻³.

An interesting feature of the present invention is the role played bythe gaseous precursors (19) from polymeric sources, in the deposition ofthe thin films of silicon carbide. This process is based on thepolymeric source being first cracked to produce large molecular weightgaseous precursor with pre-existing silicon-carbon bonds. These providethe building blocks for the silicon carbide thin film to be deposited onthe desired substrate.

Another principle of the proposed method is to create at the outset, inthe gas phase, the majority of the required bonds that will constitutethe solid silicon carbide. Consequently, the role of the chemicalreactions occurring on the substrate is drastically limited to thecompletion of the remaining small number of bonds required for thesilicon carbide structure. This technique permits much lower operatingtemperature during growth of the silicon carbide thin film than standardindustrial practices. This technique facilitates a high rate of masstransfer during desublimation of the large precursor molecules, therebyincreasing the growth rate of silicon carbide on the substrate. Thelower operating temperature provides an environment for lowering theamount of unintentional impurities in the deposited film. Desublimationis herein defined as a change of phase from a gaseous species directlyto a solid species.

The PA-CVD process takes full advantage of the Si—C and Si-N bondspre-existing in the primary polymeric source. This inventionincorporates the theoretical concept of “anticeramic yield” of thegaseous precursors: the traditional method for producing silicon carbidefrom polymeric sources is through rearrangement of the solid residueleft after pyrolysis of the precursor sources, with a ceramic yieldamounting to 80% solid; recent efforts are towards maximization of theamount of polymer remaining solid, thereby increasing the yield tohigher values. The theory applying to the new concept generally involvesthe opposite: to maximize the fraction of polymer that is vaporized forthe formation of the desired new gaseous precursor leading to theamorphous silicon carbide deposit, almost the entire polymer source isvaporized, with the net result that the ceramic yield is almost nilwhile the polymer transforms itself into a new gaseous source resultingin almost 100% anticeramic yield.

In the PA-CVD process as represented in FIG. 2, the first phase of thedeposition involves significantly higher a-SiC deposition rates comparedto the CVD method because of chemically-synchronized Si—C bondredistribution in organo-polysilanes. Still referring to FIG. 2, in thefirst chemical reaction (15), a thermally activated methylene insertioninto silicon-silicon bonds takes place to produce poly(carbosilane)precursor. This intramolecular reaction, known as the Kumadarearrangement, (Shiina, K.; Kumada, M. (1958) in J. Org. Chem, 23, 139),provides the structural framework of silicon carbide, (Scarlete, M.;Brienne, S.; Butter, S. S. and Harrod, J. F. (1994), Chem. Mater., 6,977). By simply heating the polymer precursor, a very large number ofSi—C bonds are appropriately redistributed at a very fast rate.

The second reaction (16), also represented in FIG. 2, leads to theintroduction of nitrogen atoms as donor impurities into the siliconcarbon precursors. The formation of the aminocarbosilane precursor inreaction (16), occurs via a reaction with ammonia, found either in theatmosphere or in the polymer derived source.

While still referring to FIG. 2, the third reaction (17), results inhigh molecular weight species through the formation of secondary aminespecies, leading to increased desublimation capacity. The formation ofthe secondary amine species is via the Si—H/N—H dehydrogenation. Thefourth reaction (18), governs the formation of the film derived from thethird reaction (17) onto the substrate (6). The formation of highmolecular mass ternary amine species, which are direct precursors of then-type a-SiC film on the substrate via desublimation, with the reaction(18) presented in FIG. 2 being a transamination reaction, and thisreaction being illustrative of one possible chemical mechanisms.

The temperature in the furnace varies between 100° C. and 1000° C.depending on the stage and the specific local requirements of theprocess steps in the aforementioned reactions. The gaseous species aremonitored by FT-IR spectroscopy (7) of samples extracted near thereactor outlet (9). The a-SiC thin films can also be characterized by IRspectroscopy while the concentration of adventitious oxygen in the thinfilm can be measured by using a Czochralski (Scarlete, M., J.Electrochem. Soc., (1992), 139 (4), 1207), silicon window as a standard.

In this method, gaseous precursors from polymeric sources are producedfirst, contrary to the classical polymeric route. A definite advantageof this process is a purification that involves the polymer sourceduring the sublimation process.

This purification occurs during PA-CVD, the effect of adventitiousoxidation of the initial solid polymeric source is reduced by thedecreased capacity of oxidized backbones to produce volatile material(e.g., at the limit, a high degree of oxidation produces SiO₂ withnegligible volatility). The oxidized material is therefore concentratedin the solid residue, while the precursors reaching the substrate arepurified this way. This purification helps to produce films that havevery few chemical impurities and consequently fewer surface defects.

FIG. 3 shows the various types of substrates that can be coated, as wellas, their nature and complexity with a-SiC film deposited by the processof this invention. The a-SiC thin film can be deposited on a regularceramic material of a complicated shape, quartz, electronic-gradesintered alumina, polished alumina, silicon single crystal wafer,graphite, and other commonly available and relatively inexpensivematerials. Several of the materials have been coated with the PA-CVDmethod of the invention on one side (the dark surface) while the otherside was masked during deposition and the mask removed leaving the palesurface which can also be seen in FIG. 3. Therefore, the PA-CVD methodis also compatible with conventional techniques such as maskingunderstood by those skilled in the art.

Referring to FIG. 4, the in situ FT-IR spectrum analysis of a gaseousprecursor at the outlet (9), of the reactor (2), shows the numerouspeaks that correspond to the SiH bonds formed when chemical change inthe structure of the solid polymeric source produces a polymer derivedprecursor (19). The increasing temperature near the inlet of the reactor(2), breaks down the polymeric source into various subunits to producethe gaseous precursor (19).

Referring to FIG. 5, where there is represented a schematic of FT-IRcell based on a silicon single crystal wafer (68), which is designed forthe monitoring of a PA-CVD film (8) deposited on a substrate (6) by theprocess of the invention. The substrate (6) with a coating (8) is heldin place, the thickness of the deposited layer has been exaggerated sothat the upper half and lower half of the FT-IR cell actually sit one ontop of the other and are sealed by the represented O-ring (67). There isa protective gas swept through the FT-IR cell from an inlet (64) to anoutlet (65), which maintains the appropriate inert atmosphere. The IRbeam (61) is projected onto the substrate and it is bent and reflectedthrough the deposited film (8), and the collected through a microscopeobjective (62) and detected by a MCT (mercury—cadmium—tellurium,Hg—Cd—Te) detector (63). The

FT-IR cell is mounted on an adjustable 2D micrometric stand which allowsthe FT-IR to be adjusted appropriately with respect to the IR beam (61).

Referring to FIG. 6, the carrier properties of an n-type PA-CVD filmproduced are represented. The graph represents the donor concentration,n (cm⁻³) versus the width of the depletion zone, w (μm). We observe thatthe sample tested has a low donor concentration which can be below 10¹³but range to 10¹⁵ cm⁻³ in the of the graph. A preferred range that isless than 10¹⁴ cm⁻³. These low donor level values are before any doping.The width of the depletion zone (W) which is measured in (μm) is afunction of the material connected at the junction, in the case of FIG.6, that of an n-type film with the substrate. W must not be confusedwith the film thickness. Thicker films (above 20 μm) were required forthe method of detection used to quantify the carrier concentration inthe depletion zone, and the thin films obtained by this method (100 Å to0.1 μm) will have the same type of curve as found in FIG. 6, at the farlower thicknesses.

FIG. 7 represents the semiconductor properties of an n-SiC PA-CVD filmwhich is a qualitative indication of the quality of the film, indicatedby the curve of current versus voltage.

Referring to FIG. 8, there is represented an FT-IR spectrum of a PA-CVDfilm of deposited silicon nitride. The main peak around 800 cm⁻¹ beingthat of Si—N.

Referring to FIG. 9, which represents the FT-IR spectrum of PA-CVD filmsof a synthesized silicon oxycarbide with each of the three samples (a),(b) and (c) exposed to a temperature maximum of 1100° C. but annealedfor the progressively increasing time periods of 8, 16 and 24 hoursrespectively. It must be noted, that the interstitial oxygen peak foundin sample (a) at approximately 1100 cm−1, increases as the film isannealed for longer periods. This indicates the conversion limitedresistance of the film to oxidation.

Referring to FIG. 10, there is represented a simple Schottky solar cell.The cell comprises one layer only of a-SiC (22), a metallic substrate(20) acting as anode (when layer (22) is n-type) or cathode (when layer(22) is p-type). The suitable metal is an inexpensive conductivematerial and its thickness or uniformity of thickness is not critical(viz. aluminum foil). The ohmic contact layer (21) deposited by physicalevaporation or other physico-chemical means, providing effective contactwith the overlying semiconductor layer as well as the underlyingmetallic substrate, consisting of aluminum or similar conductor (200 nm)if n-type, or aluminum/nickel (100 nm/100 nm) if p-type; the surface ofwhich must be cleaned by chemical etching or mechanical means to avoidoxidation with respect to layer (22). Alternatively, layers (21) and(22) could be made or fabricated as one composite layer over which layer(22) could be deposited. The semiconductor layer of a-SiC of n- orp-type (22), with free carrier density between 10¹⁴ and 10¹⁷ cm⁻³, of0.2 to 1 μm thickness, being the critical element resulting from thePA-CVD process and acting as the heart of the cell, with the upper freecarrier capacity being a critical factor. The top layer gold (Au) layer(23) of 5 to 10 nm thickness, acting as cathode if the semiconductor isn-type or as anode if it is p-type. The gold deposited mechanically orchemically onto n-type semiconductor. The gold layer is sufficientlythin as to allow light to reach the semiconductor.

FIG. 11 is a p-n junction barrier photovoltaic cell based on a-SiC withthe multiple layers produced by the process of the invention. In thisphotovoltaic cell, a metallic substrate is acting as an anode (24).Layer (25) is a metallised (aluminum) ohmic contact layer (˜100 nm).These layers are followed by an n-type a-SiC (˜750 nm) layer (26),p-type a-SiC (˜250 nm) layer (27), a nickel ohmic layer (28) and analuminum top contact layer (29) serving as cathode which coversapproximately 10 percent of illuminated surface.

FIG. 12 represents a stacked p-n junction solar cell, the multiplelayers produced by the method of the invention. The layers of FIG. 12(with reference numbers followed by the layer thicknesses, listed frombottom to top) are: (30) metallic substrate acting as cathode; (31)aluminum-nickel ohmic contact layer (˜100 nm/˜100 nm); (32) p-type a-Gelayer (˜200 nm); (33) n-type a-Ge layer (˜200 nm); (34) p-type a-Si(˜200 nm); (35) n-type a-Si (˜200 nm); (36) p-type a-SiC (˜200 nm): (37)n-type a-SiC (˜200 nm); and (38) top aluminum anode contact, coveringabout 10 percent of the surface.

In any semiconductor junction, such as in a Schottky junction shown FIG.13 b or a p-n junction such as shown in FIG. 14B, there is an internalelectrical field, E_(bi), called “built-in electrical field”, thatprevents the charge carriers (electrons and holes) to stay in the aregion of the material called the “depleted zone.” If the depletionregion of thickness W, is illuminated by photons with energies greaterthan (E_(c)-E_(v)), this region develops pairs of “electron-hole” whichare separated by the internal electrical field: the electrons areattracted towards the semiconductor while holes are directed towards themetal, creating a photocurrent when the device is connected to anexternal load. The structure is called a photovoltaic cell or solarcell.

The current generated in an amorphous semiconductor is mainly due to adrift component, because the diffusion component is not significant dueto low mobilities of the charge carriers. In order to collectefficiently the photon energies in an amorphous semiconductor junction,the depleted region width must be as large as possible. The depletedzone width, W, is given by:W=(εV _(bi) /q N _(D))^(1/2)where ε is the dielectric constant of the semiconductor, q is theelectron charge, N_(D) is the electron concentration, and V_(bi) is thebuilt-in voltage given by:V _(bi)=(Φ_(B)−(E_(C)−E_(F)))

The width of the depletion region can be increased by lowering the freecarrier concentration of the material.

If a p-n junction (FIG. 14) is used instead of a Schottky one, thedepletion region width can be increased (in this case, each type ofmaterial has its own depleted zone), therefore increasing the efficiencyof the photovoltaic cell.

In the Schottky structure (FIG. 11), the energy band diagram is shown inFIG. 13B before the intimate contact between the metal and thesemiconductor. The work function, Φ_(s) (41 s) is the energy differencebetween the vacuum level (39) and the Fermi level, E_(F) (40). Thevacuum level (39) is the zone where the electron is free from thesemiconductor atoms and has no kinetic energy. In elemental solids suchas a metal, represented in FIG. 13A, the values of the work functionΦ_(m) (41 m) are well established, (see for example Weast, R. C. (1990),CRC Handbook of Chemistry and Physics, 70th Edition, CRC Press, E-93).

FIG. 13B illustrates the work function of a semiconductor (41 s)normally denoted by Φ_(s). The energy difference between the vacuumlevel (39) and the bottom of the conduction band (42), denoting electronaffinity (χ), is used as reference since the Fermi level depends on thecarrier concentration in the semiconductor. However, Φ_(s) stillrepresents the energy required to remove an electron from thesemiconductor. Referring to FIG. 10 and 13B, the conduction level (42)E_(c), the valence level (43) E_(v); the affinity (44) _(χ); the workfunction (45) Φ_(s); and the energy gap (46) E_(G) are of thesemiconductor layer (22).

The Fermi level represents the energy for which the probability to finda free electron, in equilibrium and near zero Kelvin equals 0.5. Theprobability of finding an electron at a given energy level is obtainedaccording to the Fermi-Dirac function:F(E)=1+[1+exp (E−E _(F))/kT]

The Fermi level in a semiconductor depends on the free carrierconcentration, and it is closer to the conduction band than the valenceband in n-type semiconductor. Assuming that (Φ_(m)>Φ_(s), and that themetal-semiconductor system at equilibrium of FIG. 14A, the Fermi levelis at the same both in the metal and the semiconductor. Therefore, aninternally built-in electric field (E_(bi)) develops between the metaland the semiconductor. The field is oriented from the positive chargesto the negative charges, that is, towards the metal. The resultingbuilt-in voltage is equal to [(Φm−Φs)/q]. A depletion layer, ofthickness W (53 b), is formed where there are no free charges. Thepotential energy barrier for electrons moving from the metal to thesemi-conduction is known as the Schottky barrier height, Φ_(B), and isgiven by: (Φ_(B)=(Φ_(m)−χ). Under reverse bias or zero bias electricalconditions, there is no net current flowing through themetal-semiconductor junction.

For photon energies greater than E_(G); the electron-hole pairs aregenerated in the depleted zone.

In the p-n structure of FIG. 14B, where the p-type a-SiC (47) and then-type a-SiC (48) are represented. The principal electronic phenomenatakes place in the depleted zones (52) and (53). In this case, thebuilt-in voltage V_(bi) depends on the carrier concentration in thesemiconductor:V _(bi)=(kT/q)Ln(N _(A) N _(D) /n _(i) ²)where k is the Boltzmann constant, T the temperature, N_(A) the holeconcentration and n_(i) the intrinsic carrier concentration.

The depletion region widths are given by:W _(n)=(εV _(bi) /q N _(D))^(1/2)W _(p)=(εV _(bi) /q N _(A))^(1/2)

With the conduction level (49) E_(c), the Fermi Level (50) E_(F) and thevalence level (51) also represented in FIG. 14B.

The examples selected below present tailored PACVD processes for the useof some of the mentioned polymers in the synthesis of the previouslymentioned materials.

EXAMPLE 1 Use of Polysilanes as PA-CVD Precursors to n-typeSemiconductor a-SiC.

The anticeramic yield is optimized with respect to the average molecularweight and the polydispersity of the polysilane raw material. In thefirst step, an appropriate time-dependent temperature gradient isprogrammed in the furnace, so that quantitative polycarbosilaneformation is promoted. Possible ranges for the gradients are 1-10 Kmin⁻¹and 3-50 Kcm⁻¹ in a 2 inch/150 cm horizontal quartz reactor (11). Asecond step involves polycarbosilane pyrolysis that may be coupled witha nitrogen-doping process, via a carefully monitored (flow, pressure(3), and FT-IR (7)) reaction with electronic-grade ammonia (12), at apartial pressure level of 10⁻⁶-10⁻¹ torr in a UHP-Ar (or N₂) carrierflow. The resulting polymeric gaseous species (17,18) are transported inthe deposition zone (13), where they are desublimed onto the substrate(6) that can be placed in a horizontal, vertical or a tilted position,and can be mobile or immobile during the deposition. The resultedmaterial is an n-type a-SiC with a donor concentration in the range of10¹⁴-10¹⁷ cm⁻³. The thickness of the resulted film can be adjusted inthe 100 Å-1 μm range, via single/multiple layered deposition.

EXAMPLE 2 Use of Polysilanes as PA-CVD Precursors for the Synthesis ofThin Films of Passivating SiO_(x)C_(y)-glasses

Silicon oxycarbide (SiO_(x)C_(y)) is an amorphous metastable phasewherein the silicon atoms are bonded to oxygen and carbonsimultaneously. In silicon oxycarbides, high temperature properties andchemical stability have been reported, exceeding those of ordinaryvitreous silica. Silicon oxycarbide materials have also the potentialfor use in a variety of protective applications within the semiconductorindustry. Using PA-CVD technique, silicon oxycarbides of variouscompositions have been deposited on highly resistive single crystalsilicon wafers, using different conditions to vary the oxygen content inthe films. The anticeramic yield is optimized with respect to theaverage molecular weight and the polydispersity of the polysilane rawmaterial.

In the first step, an appropriate time-dependent temperature gradient isprogrammed in the furnace to enhance quantitative polycarbosilaneformation. Possible ranges for the gradients are 1-10 Kmin⁻¹ and 3-50Kcm⁻¹ in a 2 inch/150 cm horizontal quartz reactor (11). The resultedpolymeric gaseous species (17,18) are transported in the deposition zone(13).

A third step involves polycarbosilane controlled oxidation process, viaa carefully monitored [(flow, pressure (3), and FT-IR (7)] reaction withoxygen carrying species including, but not limited to, 0 ₂, 0 ₃, CO(zone 12, FIG. 1), at a partial pressure level of 10⁻⁴-10−1 torr in aUHP-Ar (or N₂) carrier flow. The oxygen carrying species are introduceddirectly in the deposition zone (13).

The controlled oxidation products are desublimed onto the substrate (6),that can be placed in a horizontal, vertical or a tilted position, canbe mobile or immobile during the deposition. The resulted material is aSiO_(x)C_(y) glass with an oxygen content in the range from x=10⁻³ tox=1.3 (measured using an external standard of Cz-silicon single crystalvia ASTM F-1188). The thickness of the resulted film can be adjusted inthe 100 Å-1 μm range, via single/multiple layered deposition.

EXAMPLE 3 Use of Polysilanes as PA-CVD Precursors to Dielectric orPassivating a-Si_(x)N_(y) Thin Films

The anticeramic yield is optimized with respect to the average molecularweight and the polydispersity of the polysilane raw material. Anappropriate time-dependent temperature gradient is programmed in thefurnace, so that quantitative polysilazane formation is promoted.Possible ranges for the gradients are 1-5° K. min⁻¹ and 3-50° K. cm⁻¹where the temperature increases (11) in a 2 inch/150 cm horizontalquartz reactor (2). A second step involves pyrolysis of the polysilazanein the reaction zone (12) in FIG. 1 where the temperature is relativelyconstant. This step may be optionally followed by a transaminationprocesses induced directly in the deposition zone (13), via a carefullymonitored (flow, pressure—parameters (3) and PID temperature parameters(5) where P=1-25, I=10-250, and D=0.1-10) reaction under pureelectronic-grade gaseous ammonia introduced in the temperature zone(11), FIG. 1 b, at a pressure level of 1-50 torr over the atmosphericpressure. The resulted precursor gaseous species (17,18) are transportedin the deposition zone (13), where they are desublimed onto thesubstrate (6), that can be placed in a horizontal, vertical or a tiltedposition, can be mobile or immobile during the deposition. Function ofthe parameters mentioned above, the resulted material is a-Si_(x)N_(y),with a x/y ratio in the range of 0.75 to 1. The thickness of theresulted film can be adjusted in the 100 Å-1 μm, via single/multiplelayered deposition.

EXAMPLE 4 Measurement of Free-charge Carrier Concentration of n-typea-SiC Films

The free-charge carriers in n-type semiconductor a-SiC films aremeasured by the capacitance-voltage (CV) method (Schroder. D. K. (1990),Semiconductor Materials and Device Characterization, Wiley Intersciencep. 41) using the Schumberger impedance analyzer Solartron 3200. Thevoltage is varied between −6 and 0 V, and the resulting capacitance isobserved to increase with increasing voltages. On sample 01-S0001, sixSchottky diodes are fabricated using mercury as anode metal: the mercuryprobe used provides a diode area of 0.453 mm². The capacitance is givenby:C=εA/wwhere A is the diode area. In the presence of an applied voltage V, thedepletion region width is given by:W=((ε(V _(bi) −V))/q N _(D))^(1/2)

The derived values for N_(D) (electron concentration) in the diodes are9 10¹⁷±0.2 10¹⁷ cm⁻³.

EXAMPLE 5 Measurement of Electron Mobilities in n-type a-SiC Films

The electron mobilities are measured in three samples 21/NO/2001/05, 06and 07, using the Van der Pauw method (Van der Pauw, L. J. (1958), Amethod of measuring specific resistivity and Hall coefficient onlamellae of arbitrary shape, Phil. Tech. Rev., vol. 20, p.220). Themeasured mobilities are defined as Hall mobilities because the techniqueis based on the Hall effect. The measurements are carried out with acurrent of 1 mA, and a magnetic field of 5 kG. The correction factors fderived for the three samples are 0.99, 0.67, and 0.86, respectively.The derived resistivities are 29.75, 22.32 and 17.24 Ωcm⁻¹, and thederived mobilities are 6.72, 4.48 and 23.19 cm²V⁻¹s⁻¹, and the electronconcentrations in the samples are calculated using the resistivity andmobility as: 3.12×10¹⁶, 6.25×10¹⁶, and 1.56×10¹⁶ cm3, respectively.

The above description and drawings are only illustrative of preferredembodiments which achieve the objects, features and advantages of thepresent invention, and it is not intended that the present invention belimited thereto. Any modification of the present invention that comeswithin the spirit and scope of the following claims is considered partof the present invention.

1. A method of depositing a thin ceramic film onto a substratecomprising: providing a polymeric source, the polymeric sourcecomprising chains, volatilizing the polymeric source in a heating zone;providing the substrate in a deposition zone; heating the polymericsource under a gaseous atmosphere having a pressure and a flowrate in apyrolysis zone, whereby pyrolyzing the polymeric source to produce agaseous precursor at a first temperature comprising said chains of thepolymeric source; positioning the substrate in the deposition zone toreceive the gaseous precursors carried by the gaseous atmosphere; andcooling the substrate at a second temperature in the deposition zonebelow the first temperature whereby desublimating the gaseous precursoronto the substrate, the precursor chemically rearranging and annealingto produce the film on the substrate, the film having properties thatinclude an amorphous nature, a crystallinity and a degree ofreticulation.
 2. The method according to claim 1, wherein the polymericsource is a silicon-based polymer.
 3. The method of claim 1, wherein thepolymeric source is a boron nitride polymer.
 4. The method of claim 1,wherein the polymeric source is a carbon nitride polymer.
 5. The methodaccording to claim 1 wherein the polymeric source comprises Si, C, N orO substituents.
 6. The method according to claim 1, wherein the film hasa thickness of at least 100 Å.
 7. The method according to claim 2,wherein the silicon-based polymer is selected from the group consistingof polysilanes, polycarbosilanes, polycarbosilazanes, polysiloxanes andpolysiloxazanes.
 8. The method according to claim 1, further comprisinga second annealing with a gaseous reactant wherein at least one of thecrystallinity or the degree of reticulation is increased.
 9. The methodaccording to claim 1, wherein the film produced is a semiconductor filmwith a donor concentration is less than 10¹⁵ cm⁻³ in a depletion zonenext to the substrate prior to doping.
 10. The method according to claim9, wherein the donor concentration is in a range from 10¹³ to 10¹⁵ cm⁻³in the depletion zone prior to doping.
 11. The method according to anyclaim 1, wherein heating the precursor is performed by a techniqueselected from the group consisting of electrical heating, UVirradiation, IR irradiation, microwave power, X-ray irradiation,electronic beams and laser beams.
 12. The method according to claim 1,wherein the gaseous atmosphere is one of an inert atmosphere and theinert atmosphere in a mixture including a gaseous reactant.
 13. Themethod according to claim 12, wherein the inert atmosphere is selectedfrom Ar and N₂.
 14. The method according to claim 12, wherein thegaseous reactant is selected from the group consisting of BH₃, B₂H₆,NH₃, PH₃, AsH₃, BCl₃, B₂Cl₆, NCl₃, PCl₃, AsCl₃, CO, O₂, O₃, CO₂, and H₂pure or in a mixture with the inert atmosphere.
 15. The method accordingto claim 1, wherein the substrate is selected from the group consistingof single crystal silicon, polycrystalline silicon, amorphous silicon,quartz, graphite, electronic-grade ceramic material, refractive ceramicmaterial, metal, alumina, sintered oxides, sintered nitrides andsintered phosphides.
 16. The method according to claim 1, wherein thefirst temperature is a maximum of 1000° C. and the second temperature isat least 100° C.
 17. The method according to claim 16, wherein the firsttemperature is a maximum of 450° C. and the second temperature is atleast 200° C.
 18. A ceramic thin film deposited on a substratecomprising chains from a polymeric source that have been deposited onthe substrate and chemically rearranged and annealed wherein the film isessentially free of defects.
 19. The film according to claim 18, whereinthe polymeric source is a silicon-based polymer.
 20. The film accordingto claim 18, wherein the polymeric source is a boron nitride polymer.21. The film according to claim 18, wherein the polymeric source is acarbon nitride polymer.
 22. The film according to claim 18, wherein thepolymeric source comprises Si, C, N or O substituents.
 23. The filmaccording to claim 18, wherein the film has a thickness of at least 100Å.
 24. The film according to claim 18, wherein the film in a singular ormultiple layer includes a donor concentration of less than 10¹⁵ cm⁻³ ina depletion zone next to the substrate prior to doping.
 25. Asemiconductor device comprising the film according to claim
 18. 26. Thesemiconductor device according to claim 25, wherein the device is ap-type or an n-type.
 27. The semiconductor device according to claim 25,wherein the device is selected from the group consisting of a solarcell, light-emitting diode, Schottky diode, a transistor, aphotothyristor and an integrated monolithic device on a single chip. 28.The method according to claim 1, wherein the polymeric source istransported through a gas inlet by the gaseous atmosphere.
 29. The filmaccording to claim 18, wherein the polymeric source is transportedthrough a gas inlet by the gaseous atmosphere.
 30. The method ofaccording to claim 2, wherein the silicon base polymer further comprisespre-existing SiC bonds that will develop a set of gaseous precursors atthe first temperature with the Si—C bonds thermodynamically stable. 31.The method according to claim 30, wherein more than 50% of the SiC bondspre-exist in the specific set of gaseous precursors.